This invention relates to X-ray lithographic techniques such as are employed in the fabrication of semiconductor devices, and in particular to an apparatus for and a method of lithographic mask alignment.
There is a requirement in the semiconductor industry for techniques that meet the demand for more complex integrated circuits. One of the major problems involved in obtaining the very high definition required is that of mask alignment with the substrate. In general a microscope is employed to observe alignment between reference marks on the mask and substrate. If an `in-contact` mask is employed there is a considerable risk of damage to both the substrate and the mask while the latter is being adjusted for correct alignment. If, however, an `out-of-contact` mask is used alignment is difficult as the spring between the mask and the substrate is generally of the order of the depth of focus of a microscope and thus limits the power of the microscope to be used for alignment.